"Had trials designed to test the question of cardiovascular toxicity directly been launched in 1999 and executed with urgency...perhaps a substantial number of deaths could have been prevented, " Drazen concludes.

FORBES: More Pain For Pfizer

Embryonic stem cells have also caught the eye of drug companies, which aim to use them to test potential drugs for effectiveness and toxicity.

FORBES: The Scientist Who Helped Stall Stem Cell Research